This invention relates to an apparatus and method for mixing a gas and a liquid. In one aspect, this invention relates to an apparatus and method for mixing a carrier gas with an atomized liquid while in another aspect, this invention relates to the formation of a mixture of carrier gas and vaporized liquid with little, if any, entrained droplets. In yet another aspect, the invention relates to an apparatus and method for applying a preservative to a perishable product.
The preservation of perishable products has been and continues to be the focus of considerable commercial interest. By extending the shelf life of a food product, e.g., a baked good, considerable economic value can be added to that product. Approaches to this end are many and varied, e.g., tight control of storage conditions, packaging, post and in situ applications of preservatives, and various combinations of these and other techniques are known and in practice to one extent or another.
In the context of baked goods, e.g., muffins, crumpets, scones, bagels, cookies, breads, etc., all of these techniques are in use, e.g., frozen or refrigerated storage, anaerobic packaging, and the addition of preservatives either to the batter or mix from which the baked good is prepared, or the application of a preservative to the finished baked good. With respect to the latter, the application of a small amount of acetic acid to a finished baked good, e.g., a crumpet, can extend the shelf life of the baked good from a typical 6-8 days to an extended 14-16 days (all other conditions, e.g., packaging, storage conditions, etc., being equal). One problem, however, in the application of a preservative to a food product is to apply the preservative in a manner that does not interfere with the natural sensient properties of the product, e.g., taste, smell, texture, etc. In the case of applying acetic acid to a finished baked product, too much acetic acid can impart an unwanted tartness to the product.
Another problem with the application of a preservative to the finished baked good is consistent application of the preservative in a production line setting. Commercially distributed baked goods, along with most other commercially manufactured and distributed perishable goods, are made in large quantities, and consistency from one item to the other is important to the commercial success of the product line. In the case of applying acetic acid to baked goods, the amount of acetic acid applied to the first baked good in the production cycle should be essentially the same as the amount of acetic acid applied to the last item in the production cycle (and all items throughout that production cycle, for that matter). This can be difficult to control over extended periods of time due to, among other things, variations in the temperature of the equipment, the preparation and delivery of the acetic acid to the finished product, and the like.
For example, the application of acetic acid as a preservative to a finished baked good typically begins with the conversion of liquid acetic acid to gaseous acetic acid. This conversion is accomplished by any one of a number of different procedures, e.g., flash evaporation, atomization, etc., and the gaseous acetic acid is then transported, typically by a carrier gas, e.g., carbon dioxide, to a treatment chamber. Finished baked goods are fed on a batch basis to the chamber in which they are exposed under predetermined conditions to the acetic acid, removed from the chamber, and then the cycle repeats. One common problem with this technique is that the gaseous acetic acid often has entrained within it small droplets of liquid acetic acid and these droplets, when deposited on the finished baked good, can constitute an overdose of preservative and impart a tartness to the product. The droplets originate from either incomplete vaporization of the acetic acid and/or as a condensate from the gaseous acetic acid as it is transported from a vaporization zone to the treatment chamber. Similar problems exist, of course, with the application of other gaseous preservatives to other perishable products.
According to this invention, an apparatus and method is provided for mixing a gas and a liquid to produce a gaseous vapor of the liquid that is substantially free of droplets. The apparatus and method are well adapted to converting a preservative from a liquid to a gaseous state for application to a perishable product.
In one embodiment, the invention is an apparatus for mixing a gas and a liquid to form a gaseous mixture substantially free of droplets, the apparatus comprising:
A. A source of the gas;
B. A source of the liquid;
C. An atomization nozzle;
D. An antechamber;
E. An orifice plate; and
F. A mixing/separation chamber.
The atomization nozzle is in fluid communication with both the source of the gas and the source of the liquid, the liquid atomized by the gas within the atomization nozzle to form an atomized mixture of the gas and the liquid. The antechamber is (i) in fluid communication with the source of the gas, and (ii) in fluid communication with and separated from the mixing/separation chamber by an orifice plate. The orifice plate comprises one or more orifices through which the gas can pass from the source of the gas, through the antechamber, and into the mixing/separation chamber. The atomization nozzle extends through the antechamber and the orifice plate, and is in open communication with the mixing/separation chamber such that the atomized mixture of the gas and the liquid is discharged into the mixing/separation chamber.
The mixing/separation chamber comprises a housing having an upper section and a lower section. The upper section is in open communication with both the atomization nozzle and the antechamber, and the lower section is equipped with an exit port. The atomization nozzle and orifice plate are configured to form a mixing zone within the upper section of the mixing/separation chamber such that as the atomized mixture of gas and liquid is discharged into the upper section of the chamber, gas from the antechamber passes through the orifices of the orifice plate so as to impinge upon and vaporize substantially all, if not all, of the liquid component of the atomized mixture of gas and liquid. The vaporized mixture of the gas and the vaporized liquid then moves into the remainder of the chamber, i.e., the separation zone of the chamber, in which any residual droplets separate gravitationally from the vaporized mixture. The residual or unvaporized droplets settle onto the floor of the chamber from which they are either removed through a drain, or vaporized if the appropriate conditions exist within the separation zone, e.g., the floor of the chamber is heated to a sufficient temperature to vaporize the droplets. The exit port located in the lower section of the mixing/separation chamber is in sealed relationship with a discharge conduit for the discharge of the vaporized mixture free of a substantial amount of residual droplets. The conduit extends from the exit port into and is in open communication with the upper section of the mixing/separation chamber. As here used, xe2x80x9cin sealed relationshipxe2x80x9d means that the discharge conduit is joined to the exit port in such a manner that the vaporized mixture can enter the conduit only from the upper section of the chamber, and it can be removed from the chamber only by passing through the conduit.
In another embodiment, the invention is a method for mixing a gas and a liquid to form a gaseous mixture substantially free of droplets, the method comprising the steps of:
A. Separating the gas into a first gas stream and a second gas stream;
B. Mixing the first gas stream with the liquid in an atomization zone under conditions in which the liquid is atomized by the gas to form an atomized mixture comprising a gas component and a liquid component, the liquid component in atomized or small droplet form;
C. Mixing the atomized mixture with the second gas stream in a mixing zone under conditions in which the liquid component of the atomized mixture is substantially vaporized to form a vaporized mixture of the gas and vaporized liquid, the vaporized mixture containing residual amounts of the liquid in droplet form;
D. Gravitationally separating the residual liquid droplets from the vaporized mixture in a separation zone; and
E. Recovering the vaporized mixture free of a substantial amount of residual droplets from the separation zone.
Typically, the mixing and separation zones are within the mixing/separation chamber previously described.
In yet another embodiment, the invention is a mixing and separation chamber for (i) preparing a gaseous mixture comprising (a) first and second gases, and (b) droplets of the second gas, and then (ii) separating the residual droplets from the first and second gases, the chamber comprising:
A. A housing having an upper section and a lower section, the upper section equipped with an entry port for receiving the first gas and an atomized mixture of the first gas and droplets of the second gas in such a manner that the first gas and the atomized mixture are in contact with one another upon their immediate entry into the upper section of the chamber, the contacting producing the gaseous mixture, and the lower section equipped with an exit port; and
B. A discharge conduit for removing the gaseous mixture free of a substantial amount of the residual droplets from the housing, the discharge conduit in a sealed relationship with the exit port and extending into the upper section of the housing.
In still another embodiment, the invention is a method of separating droplets from a vaporized mixture comprising first and second gases and droplets of the second gas, the method comprising the steps of:
A. Providing a mixing/separation chamber, the chamber comprising:
1. A housing having an upper section and a lower section, the upper section equipped with an entry port and the lower section equipped with an exit port;
2. A discharge conduit for removing from the housing the vaporized mixture free of a substantial amount of the droplets, the discharge conduit in a sealed relationship with the exit port and extending into the upper section of the housing;
B. Maintaining the chamber at a temperature above the vaporization temperature of the gases of the vaporized mixture;
C. Creating the vaporized mixture in the upper section of the housing in a mixing zone adjacent the entry port;
D. Allowing the droplets to gravitationally separate from the vaporized mixture in a separation zone of the chamber, the droplets accumulating in the lower section of the housing and the vaporized mixture free of a substantial amount of the droplets circulating throughout the separation zone; and
E. Removing the vaporized mixture free of a substantial amount of the droplets from the housing through the discharge conduit and exit port.
In another embodiment, the invention is a method of extending the shelf life of a perishable product having an external surface, the method comprising the steps of:
A. Preparing the product; and
B. Applying a vaporized preservative substantially free of droplets to the external surface of the product, the vaporized preservative prepared by a method comprising the steps of:
1. Separating a carrier gas into a first gas stream and a second gas stream;
2. Mixing the first gas stream with a liquid preservative under conditions in which the liquid is atomized by the gas to form an atomized mixture comprising the carrier gas and the liquid preservative, the preservative in droplet form;
3. Mixing the atomized mixture with the second gas stream under conditions in which the liquid preservative is substantially vaporized to form a vaporized mixture of the carrier gas, the vaporized preservative and residual droplets of the preservative; and
4. Separating the residual droplets from the vaporized mixture in a separation zone, the zone comprising:
a. A housing having an upper section and a lower section, the upper section equipped with an entry port and the lower section equipped with an exit port;
b. A discharge conduit for removing the vaporized mixture free of any significant amount of residual droplets from the housing, the discharge conduit in a sealed relationship with the exit port and extending into the upper section of the housing, the residual droplets gravitationally separated from the carrier gas and preservative vapor within the housing.
The present invention is especially well adapted for mixing gaseous carbon dioxide with liquid acetic acid to form a gaseous mixture of carbon dioxide and acetic acid which is substantially free of droplets, the gaseous mixture useful as a preservative for perishable goods, especially baked products.
As used in this specification, xe2x80x9cfree of a substantial amount of residual dropletsxe2x80x9d and like phrases means that whatever amount of residual droplets that remain in the vaporized mixture of gas (e.g., CO2) and vaporized liquid (e.g., acetic acid) after the mixture is recovered from the mixing/separation chamber, it is not enough to have a detrimental impact on the ultimate end use of the vaporized mixture. For example, if the residual droplets are acetic acid, the vaporized mixture is gaseous CO2 (as a carrier gas) and vaporous acetic acid, and its ultimate end use is as a preservative for baked goods, then the amount of residual droplets in the vaporized mixture is insufficient to have a detrimental impact on the sensient properties of the baked goods, as perceived by a typical consumer, after the goods are treated with the vaporized mixture in standard fashion.